This invention relates to methods for quickly inverting and dispersing a flocculant in aqueous slurries, such as mineral slurries, to achieve separation of solids from liquid in the slurries. In particular, this invention relates to methods for quickly inverting a liquid flocculant in-line without significantly destabilizing the emulsion that contains the flocculent. The methods employ the synergistic combination of a surfactant present in the flocculant-containing emulsion with high shear provided by, e.g., an in-line mixer, to cause the flocculant to be released for direct addition or injection to a solids and liquid separation application.
The present invention has application in, e.g., mineral and mining processing operations, paper and pulp manufacturing, reclamation processes, waste treatment, and any other suitable application requiring solid-liquid separation.
A number of industrial processes, including mining and mineral operations, conventionally rely on flocculants to help separate inorganic and organic solids from slurries so that the processing water may be recycled. Flocculants are generally organic polymers that function by aggregating the solids, either by charge neutralization or bridging mechanisms, so they settle in the slurry, resulting in a layer of settled solids and a clarified liquid, the latter being recyclable to the process. Flocculants are commercially available as water-in-oil emulsions with the flocculant polymers coiled within the water phase.
Before the flocculant can act upon the solids in the slurry, however, the emulsion must undergo inversionxe2x80x94a process wherein the bulk phase of the emulsion is inverted from oil to water and the flocculant polymer is released into an aqueous system where it can exert its flocculant activity. Inversion generally requires adding a surfactant to water and agitating the resulting mixture until the oil phase inverts. Inversion is completed when the polymeric flocculant has been released into the water.
Typically, the inversion process is both labor-intensive and time consuming, as it takes one hour or more to complete using specialized equipmentxe2x80x94such as tanks, feeders, and pumpsxe2x80x94and manpower to carefully weigh out the components and monitor the process.
U.S. Pat. No. 3,734,873 to Anderson et al. discloses a method for dissolving water-soluble vinyl addition polymers into water more rapidly than the solid form of the polymer. The method comprises preparing a water-in-oil emulsion that includes a surfactant and that inverts within one hour of being subjected to agitation. U.S. Pat. No. 5,679,740 to Heitner teaches the use of carboxylated ethoxylated nonyl phenols and alcohols as mechanically stable inverting agents for emulsion polymers. The Heitner emulsions invert after being xe2x80x9cstirredxe2x80x9d with a paddle stirrer for at least five minutes. However, neither of these methods attains an almost immediate inversion. Nor do the methods mention usage levels or high shear conditions or direct injection of the polymer to a given application. Nor do these methods eliminate the manpower, time, or equipment required by conventional methods.
Thus, there exists a continued need for a method of quickly inverting and dispersing an emulsified flocculant into a solid-liquid separation application.
This invention is directed to a method for rapidly and almost immediately inverting a flocculant-containing emulsion by the synergistic use of turbulent flow and a surfactant present in the emulsion.
In its principal aspect, a method is provided for quickly inverting a flocculant-containing emulsion and dispersing the flocculant in a slurry. The method comprises: (a) dosing water with an effective flocculating amount of at least one water-in-oil emulsion comprising at least one flocculant and at least one hydrophilic surfactant, the surfactant being present in the emulsion at a concentration of from about 1 to about 10 percent, by weight; (b) subjecting the water and the emulsion to high shear, comprising a turbulent reverse flow, at a sufficient pressure and for a sufficient time for the at least one emulsion to invert and release the at least one flocculant into the water; and (c) adding the released at least one flocculant to an aqueous slurry for separation of solids from liquid in the slurry.
In its second aspect, the invention is a method for direct injection or addition of a flocculant to a solid-liquid separation application. The method provides for quick inversion of a flocculating-containing emulsion in situ so the flocculant is released directly into the application. The method comprises feeding into an aqueous slurry an effective flocculating amount of at least one water-in-oil emulsion, each emulsion comprising at least one water-soluble organic flocculant polymer and at least one hydrophilic surfactant; and subjecting the slurry and the at least one emulsion to an effective amount of high shear for sufficient time and at sufficient pressure, such that the at least one emulsion inverts in situ and the at least one flocculant is released into the slurry for solids/liquid separation. The flocculant comprises polymers selected from the group consisting of copolymers, homopolymers and terpolymers comprising from 0.01 to 100 mole percent of any vinyl-containing functional monomer such as acrylamide or sodium acrylate, as examples. The polymers have a reduced specific viscosity of from less than 1 to about 50 deciliters per gram or greater.